Optical Properties of Dielectric Materials

For the most part, dielectrics are transparent throughout the visible spectrum, assuming their bandgap is greater than 3.8 eV (the energy of a near-ultraviolet [UV] photon). 

In the previous section we showed (Equation 24.12) that the index of refraction was simply the square root of the dielectric constant and, since the dielectric constant is a function of frequency and can become negative, the index of refraction is a function of frequency and may be complex. Summarizing, 

Having spent a fair amount of effort in Chapter 23 determining the dielectric function of dielectric materials, we are now in a position to obtain their N and K values at various wavelengths, which describe their optical properties. 

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